Spieth has always been considered a phenom. He won the U.S. Junior Amateur twice. Tiger Woods is the only other guy to ever do that.

You simply don't see 20-year-olds playing as well as Spieth has played in the last year.

It's not like he burst onto the scene with one exceptional performance. He doesn't drive the ball 350 yards (in fact, he's one of the shorter hitters on tour), and he doesn't gamble on highlight-reel shots like Bubba Watson.

His rise has been built on consistency and a week-in, week-out steadiness that young players never have.

"Spieth is inherently conservative ('the world's oldest 20-year-old,' in the words of his trainer, Damon Goddard). He finished 10th on the Tour money list—$3.9 million in just 23 starts—and along the way added lucrative deals with Titleist and Rolex, but so far his only splurge has been Dallas Cowboys season tickets. He dates his high school sweetheart, Annie Verret, a sophomore at Texas Tech and rolls in a 2008 Yukon with 110,000 miles on the odometer. Equipment companies threw money at him when he turned pro, but he waited until September to commit to Titleist because he didn't want to be tinkering with new sticks while he was chasing his Tour card. 'I don't really like change,' he says."

His rise has flown under the radar. That won't be the case if he wins on golf's biggest stage Sunday.